1. Field of the Invention
The present invention relates to an image synthesizing apparatus which is capable of synthesizing two or more images.
2. Description of the Related Art
An image synthesizing apparatus has been used for synthesizing two or more images. The image synthesizing apparatus normally performs the synthesizing of two images on the basis of the following equation (1): EQU P.times..alpha.+Q.times.(1-.alpha.) (0.ltoreq..alpha..ltoreq.1)(1)
where P and Q denote image data, respectively, and .alpha. is a constant between 0 and 1.
The actual synthesizing of two images based on the equation (1) requires the image synthesizing apparatus which is capable of manipulating a very large volume of image data. It means that the apparatus has to perform the operation quite rapidly. For the purpose, the apparatus employs a look-up table.
The known image synthesizing apparatus using the equation (1) will be described below.
The image synthesizing apparatus includes two image memories for storing respective image data P and Q, a control memory for storing the constant .alpha., a look-up table for storing conversion values for synthesizing the input image data and for outputting the conversion value corresponding to the image data P, Q and the constant .alpha. as an address, a digital-to-analog converter for converting the input digital conversion value into an analog value, and a display unit for displaying a synthesized image on the basis of the converted analog value. Because the conversion values stored in the look-up table are pre-calculated by the equation (1), it results in realizing the rapid operation for synthesizing images.
According to the construction, the image data P and Q and the constant .alpha. are read from the image memories and the control memory, respectively, and are input to the look-up table. In the look-up table, the conversion values pre-calculated by the equation (1) are stored. Then, the look-up table sends the digital conversion value corresponding to the input image data P and Q and constant .alpha. to the digital-to-analog converter in which the conversion data is converted into the analog data. Then, the converted analog data is sent to the display unit on which the synthesized image based on the analog data is displayed.
The foregoing image synthesizing apparatus known by the present inventors, however, is required to input the image data P and Q and the constant .alpha. to the look-up table at the same time. It means that the look-up table has to have a large storage capacity.
Assume that each tone number of the image data P and Q has eight (8) bits and the constant .alpha. has four (4) bits. It results in the look-up table receiving overall data of 20 bits. That is, the capacity of the look-up table is substantially as large as an image memory composed of 1024.times.1024 bits. The look-up table needs a long duration of time for setting the conversion values for synthesizing the input image data to the table itself. The setting time is substantially as long as the time in case that the image data stored in the image memories are directly converted with the conversion values calculated by the equation (1). The long setting time loses the merit of the look-up table.
It is possible to restrict the number of bits of the data to be input to the look-up table for reducing the storage capacity of the look-up table. The resulting image of the image synthesizing apparatus, however, is made inferior in quality.